1. Field of the Invention
This invention relates to belt filter presses for removing liquid from a mixture of liquid and solid material. In one aspect, the invention relates to a primary roller with radially-extending wings for a belt filter press.
2. Description of the Related Art
Belt filter presses are utilized to remove liquid from a mixture of liquid and solid material, leaving a relatively dry, solid xe2x80x9ccakexe2x80x9d for disposal or further processing. The belt filter press comprises a frame and an assembly of rollers that support and drive an upper continuous belt and a lower continuous belt that are in operable communication with each other. The belts are permeable to allow the extrusion of the liquid therethrough. The mixture is first placed on the lower belt, then xe2x80x9csandwichedxe2x80x9d between the upper and lower belts. The belts and the retained mixture then pass through a wedge section where the mixture is evenly distributed between the belts, and an initial volume of liquid is removed. The belts then pass through a series of progressively smaller diameter rollers where the retained mixture is compressed for further liquid removal. The belts are then separated and the dry xe2x80x9ccakexe2x80x9d is removed from the belts, generally by a scraping apparatus. The belts then pass through one or more belt washers, after which the process is repeated. The liquid from the extrusion and belt washing processes are collected for disposal.
The first roller that the belts contact after exiting the wedge section is typically the largest roller and extrudes the largest volume of liquid. These rollers may be either solid, or provided with channels to aid in the removal of the extruded liquid. With a solid roller, liquid that is extruded from the mixture must flow to the edges of the belts in order to be removed. With a channeled roller, the roller surface comprises discrete belt contact surfaces alternating with the channels. Pressure on the belts and retained mixture, and thus extrusion of liquid from the mixture, occurs only at the discrete belt contact surfaces. The fewer the contact surfaces, the less liquid will be extruded and the greater will be the wear on the belts. Typically, the belts pass beneath the first roller and, thus, extruded liquid falls by gravity away from the roller to be collected in an underlying container. With a channeled roller, some liquid moves toward the center of the roller as the belt travels around the roller. This liquid then must flow longitudinally to the roller ends to be removed. Some of this liquid can be retained in the interior of the roller and can be reintroduced into the belts and mixture. As well, liquid that has gradually built up in the interior of the roller can suddenly flush to the roller ends, missing the underlying container.
The invention comprises a winged primary roller for a belt filter press for removing liquid from a mixture of liquid and solid material. The belt filter press comprises two endless filter belts disposed adjacent each other so that a portion of the belts travel together and converge towards one another and between which a material is progressively compressed, and a substantially cylindrically-shaped primary roller around which the belts are compressed having a longitudinal axis and ends. The primary roller is provided with a plurality of radially extending fins, each of which has a wing at the free end thereof. The wings are arcuate and defined by a radius of curvature that is coaxial with the longitudinal axis of the roller. At least one taper piece is provided between the fins to direct fluid toward the ends of the roller. In one embodiment, the at least one taper piece between the fins has a first portion between the roller ends closer to the circumference of the roller and a second portion between the roller ends closer to the longitudinal axis of the roller. In another embodiment, the at least one taper piece between the fins has a first portion near the midpoint between the roller ends closer to the circumference of the roller and a second portion near the roller ends closer to the longitudinal axis of the roller. The at least one taper piece is triangular. At least one plate is provided adjacent to at least one end of the roller to direct liquid exiting the roller. The at least one plate is orthogonal to the longitudinal axis of the roller.